This invention relates to exhaust brake valve units, that is to say valve units adapted to be positioned in the exhaust system of an internal combustion engine so that on closure of the valve, back pressure to the engine is created, thus providing or enhancing engine braking when the engine is used for propelling a road vehicle. In view of the heat factor exhaust brake valve units are not precision built units but are built with fairly large tolerances between respective members to allow for expansion of those members as the valve is heated by the exhaust gas passing through the valve. It is for this reason that the exhaust brake valve unit of the present invention should not be confused with well known gate valves such as is disclosed in U.S. Pat. Nos. 2,896,541, 3,254,604, 3,290,003, and 3,378,224, which are used specifically for controlling the passage of fluid at very much lower temperatures than the temperatures of exhaust gases. In such gate valves it is essential to provide fluid type seals and consequently these valves have to be manufactured with a very high degree of precision. Because of this precise construction such gate valves could not possibly operate at the temperature of exhaust gases from an internal combustion engine. To further illustrate such precision gate valve units reference is also made to U.S. Pat. Nos. 2,457,930 to Smith, 2,853,268 to Hughes, 3,111,137 to Carlin, 3,175,473 to Boteler et al, 3,194,269 to Williams and 3,511,472 to Zimmerman. A similar gate valve is to be found also in British Pat. No. 1,380,462 to Scobel.
Exhaust brake valves are generally located in front of the muffler box of an exhaust system as close to the outlet manifold of an internal combustion engine as possible. This is necessary since otherwise if the exhaust brake valve was placed after the muffler box then the muffler would disintegrate upon operation of the exhaust valve because the baffles in the muffler box would be blown back and would block up the exhaust system whereupon pressure would build up in the muffler box and this would split open. Furthermore, exhaust brakes are generally used with the types of engine that are used in heavy commercial vehicles and because of the restricted space of the engine compartment it is difficult to locate them in the exhaust system close to the output manifold. A major problem arises when service engineers have to work on the exhaust brake. Because of the space restriction their work is hampered and effected less efficiently, causing the work to be very costly and time consuming.
Various constructions of exhaust brake valves have been proposed in the past, such designs including slide valves.
However, these existing exhaust brake valves have suffered from the disadvantage that they have to be dismantled from the exhaust system in their entirety for maintenance purposes which as previously mentioned involves considerable expense, particularly in the complex exhaust systems of modern engines.
Furthermore, known exhaust brake valve units are uni-directional, that is to say they are designed to be closable against exhaust flow in only one direction. Consequently such valves must be assembled in an exhaust system in the correct orientation giving scope for error during initial installation and subsequent maintainence.
One known exhaust brake is described and claimed in U.S. Pat. No. 1,577,466 in which there is shown an exhaust brake having a closure member movable transversely to the exhaust passage through the body of the exhaust brake. The exhaust brake body is of a two part construction in which the valve closure member is sandwiched between the two parts. The two parts are held together by bolts or screws and to repair the closure member the two parts must together be removed from the exhaust system and then separated to allow removal of the closure member. In British Patent Specification No. 864,508 there is disclosed an exhaust brake having a hollow body, a valve closure member slidable transversely to the axis of the exhaust passage through the high body and a fluid operable piston cylinder device connected with the exhaust brake body for moving the closure member. However, the body of the exhaust brake is made up of two or more parts which are held together by six bolts. This construction is somewhat similar to that disclosed in U.S. Pat. No. 1,577,466 and similarly to effect repair of the closure member it is necessary to release the exhaust brake from the exhaust system and then split the exhaust brake body.
It is among the objects of the present invention to provide an exhaust brake valve unit which alleviates the above disadvantages.